Blasting cap



B. J. sEvo LD BLASTING cAP Filed June 2s, 194e July 22, 1952 .dm v b b W. m a e V o S N n I. A f v-v--f-h= i. d* A Y @Wi 2 il@ 3 m g 'j l ru. .xl |I.l|.-|.|| W .ma v. r B m m 2 b b b H u d w H .b B

Fig. l

Patented July 22, 1952 BLAsTING CAPv Boyd J. Sevold, AChicago, Ill., va'ssignor to Atlas 'Powder' Company, Wilmington, Del., a. corporation of Delaware Application J une 23, 1948', Serial No. 34,622

11 (JIaims.`

"I'he present application relates to a delay electric blasting cap.

An object of the inventionlis the provision of an electric blasting capghaving a delay period between its initiationrand detonation. Y Y

'Another object of the invention is the provision o fadelay electric blasting cap having a short delaylperiod- Y further objectof theizwentionis the provision of a delay electric vblasting cap having a relatively uniform delay time. d

Other objects of the invention will be apparent from the following description. Y

,Electric blasting Vcaps usually include tubular closed metal shells intovthe bottomof which are pressed one or more detonating explosive charges. An electric ignition elemenirusually made up of a bridge wire surrounded lby a flash composition, is sealed into the top of the cap to provide a means for initiating the explosive when the cap is to be used. Y l

Sometimes it is desirable to provide a delay periodbetween the time thecap fis initiated by firing the' ignition element and the time of detonation of'the explosive in the cap. In the last few years delay electric blasting caps having delay periods Yof the Vorderdof avfew milliseconds have found considerable use. d Y

` In the -usual delay cap the/delay period is obtained byinterfposition'inga train of combustible material between the' ignition element and the detonating'explosive. ,"I'hefignition element initiates the delay train, and,`a`fter burning through, the delay train in turninitiates'the detonating explosive'.

In 'accordance with the present invention, a delay period is provided by a rupturable membrane located between an ignition element and a detonating explosive.v The electric 'ignition element is'located iny a gas-tight chamber and separated from the detonating explosive by the rupturable membrane. The membrane is provided with an unsupported portion on the side adjacent the' detonating explosive. y On actuation of the ignition element, gas pressure builds up behind the rupturable membrane until the membrane breaks permitting the llame from the ignition element to pass and to initiate the detonating exrplosive. I

A propellent fuel, such as black powder or smokeless powder, may be located adjacent the ignition element to assist the development of gas pressure. A preferred membrane material for use in the caps of this inventionis metal foil. It is easily obtained in uniform thickness; it is easily secured in the cap; and it provides desirable rupturing characteristics. Such metals asbrass, aluminum, copper, tin, zinc, gold, and silver are desirable foil materials. However, frangible plastic materials also' may be employed.

While the rupturable membrane may be secured in the 4cap by any 'convenient means, in 'a preferred embodiment -of the invention, a tubular element is tted tightly into the cap andthe membrane is positioned so as to span the tubular element.

The invention will be further understood by reference to the drawings in which:

Figure 1 is an enlarged sectional side elevational view of a delay electric blasting cap of the invention.

Figure 2 is an enlarged sectional view of av modied type of membrane assembly.

Figure 3 is an enlarged sectional View of a modiiiedarrangement of the cap parts.

` Referring to Figure 1 of the drawings, |I is a conventional detonator shell made of gilding metal and dimensioned about 0.260" in inside diameter and about 3" in length. Loaded into the bottom of shell is tetryl base charge explosivev I3. Over base charge |3 is loaded nitro'- mannite primary detonator charge I5, and on top of charge |5 is loaded -flash charge made of a mixture of diazo-dinitrophenol and nitromannite.Y Over allthese charges is placed metal inner capsule I9, and the capsule and charges are pressed against the bottom of the shell. 2| is a brass tube 0.265" in diameter which is pushed in a press fit into shell until it rests on inner capsule I9. Tube 2| is provided with a bore 0.140" in diameter and is counter-bored from the top to a diameter of 0.200. On the shoulder produced by the difference in diameter between the bore and counterbore rests brass foil diaphragm 23. Tube 25 is pushed down into the counter-bore of tube 2| in a press nt until it rests upon and secures foil 23 in gas-tight relation. Over foil 23 is placed a small charge 2l of loose black powder. Conventional match type electric ignition element 29 held in paper insulating tube 3| by poured sulphur 33 is slipped into the cap above charge 2l. In-

sulated wires 34 and 35 are connected to electric ignition element 29 and lead outside of the cap. The top of the cap is sealed by poured asphalt seal 31 and poured sulphur seal 39.

In operation of the cap electric current is applied to Wires 34 and 35. This current initiates ignition element 29 which bursts into flame thereby igniting black powder charge 2T| and except that it is counter-bored only for a short distance, and the bore is sufciently large in di-m,

ameter that the remaining wall, designated as i I,

is but 0.01" thick. After the =foil-fdesignated. asl

23a, is put in place, thin wall'li iscrim'ped ovei'xtoV secure the foil in place.

It is sometimes desirable to enlarge the. gas

space behind the membrane. Figure 3 shows 'this space enlarged by means of a tube spacerllil4 long and positioned between tube 2 Ib and insulatingtube S'Ib which contains ignitionelement'ZBb. vIt-will` be obvious thatthe invention is appli- Y cable to many types of electric blasting. caps.

The materials of the construction and the dimensions shown are only-exemplaryand maybe.

varied as is convenient. For example, many types of explosive charges, of .shell materials, land of sealing materials may be substitutedv for those'- shown,'as will be understood by those skilled'in theA art'. v

Similarly the invention may bev employedwith many different types of ignition elements. For example, the bridgek plug type, the cavityplug type, or the bead type. maybe employed inplace of the match type. illustrated;

-Inv general, the sealing means used should be sufficiently tight that adequate rupturing of the membrane takes plate. It is. not necessary for the obtention of the delay function thatI the cap be gas tight. on the side ofi the membrane where the detonating composition islocated. Howevenit is:

usually preferredthat the 'cap as a wholebe ventlessand gas tight sofas to prevent any egress of y flamefromthe cap'prior to its detonation. r g

- The membrane thickness may be variedpdependingV on` the area themembrane'is tospan, on the amount of pressure which is'built up; anclon the strength of otherpartsoftheY cap. -Thicknesses'between about :.0008 inch and about 0.003 inch are: generally satisfactory.' The free space betweenthe membrane andi thev detonating ex'- plosive need only be sui-licient to permit vadequate rupturing.

- lThe following examples illustrate specii'lc embodiments of the invention.

Example 1 54 caps were made up similar to thosedescribed in Example 1 except that no black powder was included. These had an average delayl period of 4.0 milliseconds, the longest period being rL milliseconds andthe shortest 1.0 millisecond.

y Example 3- y 1'0 caps were made up similar to that described V28caps were made up similar to that described inr connection with Figure 1 of the drawing, ex-

'ceptj' that they 4included the delay element construction:describedixin connection with Figure 2 of the drawing` in place of that shown in Fig- ,ure 1, lThe foil was 0.001'' in thickness, and 0.010

gram' of loose black powder was included over the foil: 'These caps on being detonated showed an average delay time of 4.8, milliseconds, the longest time being,8.0 milliseconds-and the shortest. time being 3.0 milliseconds.

Example 5l 23 caps were madeY up similarly. to Ythose made up in accordance. with Example 4 except, that, the foil used'was 0.002 thickness. `ill/'henthese-.caps were detonated they showed an average',delay time of 5.5 milliseconds, the longest timebeingA 8.0 milliseconds and the shortesttime beingfi. milliseconds. v i

What is claimed is.: n l

l. A delay electric.,-blastin g .capcomprisng a shell,ka gas-tight chamber \in..saidljs'hell said chamber, comprising freel space for, gasexpansiom a gas-producing electric ignition element insaid gas-tight.. chamber, said chamber including a metalr foil wall, a Adeton'ating explosive in said shell outside-of said chamber, said foil having, an unsupported portion. on the` side adjacent-.said detonating explosive and having a strength such: that it ,rupturesv due togas pressure produced on the functioning .of .saidv ignition element, thereby. permittinginitiationof saiddetonating explosive.

2. delay lelectric blasting capaccording .to claim y1 in whicha propellant powder is included plosive, said partition having an unsupported portion on the side adjacent. said detonating-l ex-l plosive andY having a strength such that it rup-` turesdue to. gas pressureproduced onthe functioning of saidv ignition element, thereby permittinginitiation of said detonating explosive.

4. A delayv electric blasting cap comprising. at snellagas-tight partition in said shell including a metal foil, a gas-producingY electricignition element sealed in a gas-tight manner in saidjshell' on one side of said partition, thereY being freev space for gasy expansion adjacent saidyignition' element, a detonating explosive in said shell `on the other side of said partition, said foil having an unsupported portion on the sidev adjacent said detonating explosive `and having-a, strength such that it ruptures due to. gas pressure produced' on the functioning of said ignition element, thereby-A permitting initiation of said detonating explosive.

5. A delay electric blasting cap according-to claim 4 in which a propellent powder is included on the side of said partition where said ignition element is located.

6. A delay electric blasting cap comprising a shell, a, gas-tight partition in said shell including a thin portion, a gas-producing electric ignition element sealed in a gas-tight manner in said shell on one side of said partition, there being free space for gas expansion adjacent said ignition element, a detonating explosive in said shell on the other side of said partition, and but for said thin portion being in direct name communication with said ignition element, said thin portion having an unsupported portion on the side adjacent said detonating explosive and having a strength such that it ruptures due to gas pressure produced on the functioning of said ignition element, thereby permitting initiation of said detonating explosive.

7. A delay electric blasting cap comprising a closed shell, a detonating explosive in said shell, a gas-producing electric ignition element in said shell. free space for gas expansion adjacent said ignition element, a tube tting in said shell in gastight relation, a metal foil spanning the inside of said tube in gas-tight relation and located between said ignition element and said explosive, said foil having an unsupported portion on the side adjacent said detonating explosive and having a strength such that it ruptures due to gas pressure produced on the functioning of said ignition element, thereby permitting initiation of said detonating explosive.

8. A delay electric blasting cap according to claim 7 in which a propellent powder is included on the side of said foil where said ignition element is located.

9. A delay electric blasting cap comprising a closed shell, a detonating explosive in said shell, a gas-producing electric ignition element in said shell, free space for gas expansion adjacent said ignition element, a tube fitting in said shell in gas-tight relation, a thin membrane spanning the inside of said tube in gas-tight relation and located between said ignition element and said explosive, so that, but for said membrane, said ignition element is in direct flame communication with said detonating explosive, said membrane having an unsupported portion on the side adjacent said detonating explosive and having a strength such that it ruptures due to gas pressure produced on functioning of said ignition element, thereby permitting initiation of said detonating explosive.

10. A delay electric blasting cap comprising a closed shell, a detonating explosive in said shell. a gas-producing electric ignition element in said shell, free space for gas expansion adjacent said ignition element, a tube fitting in said shell in gas-tight relation, the inside of said tube including a shoulder, a metal foil spanning the inside of said tube and resting on said shoulder, a second tube fitting inside said rst tube and holding said metal foil in gas-tight relation therein, said metal foil being located between said ignition element and said detonating explosive, and said foil having an unsupported portion on the side adjacent said detonating explosive and having a strength such that it ruptures due to gas pressure produced on functioning of said ignition element, thereby permitting initiation of said detonating explosive.

11. A delay electric blasting cap according to claim 10 in which a propellent powder is included in direct communication with said ignition element.

BOYD J. SEVOLD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 426,971 Tirmann Apr. 29. 1890 2,000,617 Schaler-Glossl May 7, 1935 2,429,490 Scherrer Oct. 21, 1947 FOREIGN PATENTS Number Country Date 28,532 Great Britain 1909 

